Magnetoresistive element and magnetic memory using the same

ABSTRACT

According to one embodiment, a magnetoresistive element includes the following configuration. A first magnetic layer has an invariable magnetization. A second magnetic layer has a variable magnetization. A nonmagnetic layer is provided between the first and the second magnetic layers. The first magnetic layer has a structure in which first, second and third magnetic material films and a nonmagnetic material film are stacked. The first magnetic material film is provided in contact with the nonmagnetic layer, the nonmagnetic material film is provided in contact with the first magnetic material film, the second magnetic material film is provided in contact with the nonmagnetic material film, and the third magnetic material film is provided in contact with the second magnetic material film. The second magnetic material film has a Co concentration higher than that of the first magnetic material film.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2011-148444, filed Jul. 4, 2011;the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a magnetoresistiveelement and a magnetic memory using the magnetoresistive element.

BACKGROUND

Recently, a magnetic random access memory (hereinafter referred to as anMRAM) that uses the magnetoresistive effect of a ferromagnetic body hasbeen drawing more attention as a next-generation solid-state nonvolatilememory which has a high capacity and which is capable of high-speedreading/writing and capable of operating with low power consumption. Inparticular, a magnetoresistive element having a ferromagnetic tunneljunction has been drawing attention since the discovery of a highmagnetoresistance change rate shown by the magnetoresistive element. Theferromagnetic tunnel junction has a three-layer stack structurecomprising a storage layer variable in magnetization direction, aninsulator layer, and a fixed layer which faces the storage layer andwhich maintains a predetermined magnetization direction.

This magnetoresistive element having the ferromagnetic tunnel junctionis also referred to as a magnetic tunnel junction (MTJ) element. As awriting method for this element, a writing (spin transfer torquewriting) method that uses spin-momentum-transfer (SMT) has beenproposed. According to this method, a spin-polarized current is passedthrough the magnetoresistive element to switch the magnetizationdirection of the storage layer. The amount of spin-polarized electronsto be injected may be smaller if the volume of a magnetic layer thatconstitutes the storage layer is smaller. Thus, this writing method isexpected to enable both element miniaturization and current reduction.

It has been considered to use, as a ferromagnetic material thatconstitutes the magnetoresistive element, what is known as aperpendicular magnetization film having a magnetization easy axis (anaxis of easy magnetization) in a direction perpendicular to a filmplane. When magnetocrystalline anisotropy is used in a perpendicularmagnetization configuration, shape anisotropy is not used, so that theelement shape can be smaller than that of an in-plane magnetizationconfiguration. Dispersion in a magnetization easy direction can also bereduced. Therefore, the use of a material having high magnetocrystallineanisotropy is expected to enable the maintenance of thermal disturbanceresistance and also enable both miniaturization and current reduction.

The problem that arises when the MTJ is formed by the perpendicularmagnetization type is that materials included in an underlying layer foradjusting crystal orientation and the storage layer diffuse due to aheat treatment and the magnetoresistance ratio (MR ratio) deteriorates.A technique that addresses this problem has been known. According tothis technique, a crystallization accelerating film for acceleratingcrystallization is formed in contact with an interface magnetic filmhaving an amorphous structure. Thereby, crystallization is acceleratedfrom the side of a tunnel barrier layer, and the interface between thetunnel barrier layer and the interface magnetic film is aligned toachieve a high MR ratio. The use of this technique enables a high MRratio. However, when a heat treatment associated with elementfabrication is taken into consideration, it is preferable that the MRratio (or resistance value) does not change when a heat treatment isadditionally conducted after the initial condition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a magnetoresistive element according to afirst embodiment;

FIG. 2 is a sectional view of a magnetoresistive element according to asecond embodiment;

FIG. 3 is a sectional view of a magnetoresistive element according to athird embodiment;

FIG. 4 is a sectional view of a magnetoresistive element according to afourth embodiment;

FIG. 5 is a sectional view of a magnetoresistive element according to afifth embodiment;

FIG. 6 is a sectional view of a magnetoresistive element according to asixth embodiment;

FIG. 7 is a graph showing the Pd concentration dependence ofperpendicular magnetic anisotropy in a storage layer;

FIGS. 8A and 8B are graphs showing the thickness dependence and heattreatment temperature dependence of a TMR ratio according to theembodiment;

FIG. 9 is a sectional view of a stack structure including an underlyinglayer and a storage layer in the magnetoresistive element according tothe embodiment;

FIG. 10 is a circuit diagram showing the configuration of an MRAMaccording to a seventh embodiment;

FIG. 11 is a sectional view of a memory cell in the MRAM according tothe seventh embodiment;

FIG. 12 is a block diagram showing a DSL data path unit of a DSL modemas an application example;

FIG. 13 is a block diagram showing a cell phone terminal as anapplication example;

FIG. 14 is a top view of an MRAM card as an application example;

FIG. 15 is a plan view of a card insertion type transfer apparatus as anapplication example;

FIG. 16 is a sectional view of the card insertion type transferapparatus as an application example;

FIG. 17 is a sectional view of a fitting type transfer apparatus as anapplication example; and

FIG. 18 is a sectional view of a sliding type transfer apparatus as anapplication example.

DETAILED DESCRIPTION

Components having substantially the same functions and configurationsare provided with the same reference signs in the following explanationsand are repeatedly described only when necessary. It is to be noted thatthe drawings are schematic and that the relation between the thicknessand planar dimensions, the ratio of the thickness of layers, etc. aredifferent from real ones. Therefore, the following description should beconsidered to judge specific thickness and dimensions. It is also to benoted that the drawings include parts different in the relation andratio of their dimensions.

In general, according to one embodiment, a magnetoresistive elementincludes a first magnetic layer, a second magnetic layer and anonmagnetic layer. The first magnetic layer has an axis of easymagnetization perpendicular to a film plane, and an invariablemagnetization direction. The second magnetic layer has an axis of easymagnetization perpendicular to a film plane, and a variablemagnetization direction. The nonmagnetic layer is provided between thefirst magnetic layer and the second magnetic layer. The first magneticlayer has a structure in which a first magnetic material film, anonmagnetic material film, a second magnetic material film, and a thirdmagnetic material film are stacked. The first magnetic material film isprovided in contact with the nonmagnetic layer, the nonmagnetic materialfilm is provided in contact with the first magnetic material film, thesecond magnetic material film is provided in contact with thenonmagnetic material film, and the third magnetic material film isprovided in contact with the second magnetic material film. The secondmagnetic material film has a Co concentration higher than that of thefirst magnetic material film. A current is passed across the firstmagnetic layer and the second magnetic layer via the nonmagnetic layerso that the magnetization direction of the second magnetic layer varies.

First Embodiment

FIG. 1 is a sectional view of a magnetoresistive element according tothe first embodiment.

In sectional views in and after FIG. 1, arrows indicate magnetizationdirections. The magnetoresistive element in the present specificationand claims means a tunneling magnetoresistive (TMR) element that uses asemiconductor or an insulator as a tunnel barrier layer. Although themain components of the magnetoresistive element are shown in thesectional views in and after FIG. 1, more layers may be included as faras the shown configurations are included.

Writing is performed in a magnetoresistive element 1 by a spin transfertorque magnetization reversal method. That is, the magnetoresistiveelement 1 changes the relative angle between the magnetizations of astorage layer and a fixed layer into a parallel or antiparallel state(i.e., minimum or maximum resistance) in accordance with the directionof a spin-polarized current which is passed through each layer in adirection perpendicular to a film plane. The magnetoresistive element 1thus associates the state with binary information “0” or “1” and therebystores the information.

As shown in FIG. 1, the magnetoresistive element 1 includes at least twomagnetic layers 2 and 3, and a nonmagnetic layer 4 provided between themagnetic layer 2 and the magnetic layer 3. The magnetic layer 3 isprovided on an underlying layer 5, and has a magnetization easy axis inthe direction perpendicular to the film plane. The magnetizationdirection of the magnetic layer 3 is variable. Here, the variablemagnetization direction means that the magnetization direction changesbefore and after writing. In the present specification, the film planemeans the upper surface of a target layer. Hereinafter, the magneticlayer 3 is referred to as a storage layer (free layer, magnetizationfree layer, magnetization variable layer, or recording layer). Detailedproperties of the storage layer 3 will be described later. Themagnetization in the direction perpendicular to the film plane isreferred to as perpendicular magnetization.

The magnetic layer 2 has a magnetization easy axis in the directionperpendicular to the film plane, and its magnetization direction isinvariable in contrast to the storage layer 3. Here, the invariablemagnetization direction means that the magnetization direction does notchange before and after writing. Hereinafter, the magnetic layer 2 isreferred to as a fixed layer (magnetization fixed layer, referencelayer, pin layer, standard layer, or magnetization standard layer). Thefixed layer 2 according to the present embodiment has a structure inwhich a first magnetic material film 2 a, a nonmagnetic material film 2b, a second magnetic material film 2 c, and a third magnetic materialfilm 2 d are stacked in this order from the side contacting thenonmagnetic layer 4.

When a structure is regarded as essentially equivalent to the structureaccording to the present embodiment, the names of the components thereinare not limited to the above-mentioned names. Detailed properties of thefixed layer 2 will be described later. The magnetization direction ofthe fixed layer 2 is, by way of example, opposite (upward) to an unshownsubstrate provided under the underlying layer 5 in FIG. 1, but may betoward (downward) the substrate.

The nonmagnetic layer 4 is also referred to as a tunnel barrier layer,and is made of an insulating film of, for example, an oxide. Detailedproperties of the nonmagnetic layer 4 will be described later. Themagnetoresistive element 1 according to the present embodiment is amagnetoresistive element used for the spin transfer torque writingmethod. That is, in writing, a current is passed from the fixed layer 2to the storage layer 3 or from the storage layer 3 to the fixed layer 2in the direction perpendicular to the film plane such that electronshaving spin information are transferred from the fixed layer 2 to thestorage layer 3. The spin angular momentum of the transferred electronsis moved to the electrons in the storage layer 3 in accordance with theconservation law of the spin angular momentum such that themagnetization of the storage layer 3 is switched.

For example, when the magnetization direction of the storage layer 3 isantiparallel to the magnetization direction of the fixed layer 2, acurrent is passed from the storage layer 3 to the fixed layer 2. In thiscase, electrons run from the fixed layer 2 to the storage layer 3. Atthis moment, electrons spin-polarized by the fixed layer 2 runs to thestorage layer 3 through the nonmagnetic layer 4, and the spin angularmomentum is moved to the storage layer 3 so that the magnetizationdirection of the storage layer 3 is switched and becomes parallel to themagnetization direction of the fixed layer 2.

On the other hand, when the magnetization direction of the storage layer3 is parallel to the magnetization direction of the fixed layer 2, acurrent is passed from the fixed layer 2 to the storage layer 3. In thiscase, electrons run from the storage layer 3 to the fixed layer 2. Atthis moment, electrons spin-polarized by the storage layer 3 run to thefixed layer 2 through the nonmagnetic layer 4, and electrons having thesame spin as the magnetization direction of the fixed layer 2 passthrough the fixed layer 2. However, electrons having a spin opposite tothe magnetization direction of the fixed layer 2 are reflected at theinterface between the nonmagnetic layer 4 and the fixed layer 2, and runto the storage layer 3 through the nonmagnetic layer 4. As a result, thespin angular momentum is moved to the storage layer 3 so that themagnetization direction of the storage layer 3 is switched and becomesantiparallel to the magnetization direction of the fixed layer 2.

In order to read information from the magnetoresistive element 1, a readcurrent that does not switch the magnetization of the storage layer 3 ispassed across the storage layer 3 and the fixed layer 2 through thenonmagnetic layer 4. Thus, the information can be read from themagnetoresistive element 1.

The magnetoresistive element 1 according to the first embodiment shownin FIG. 1 shows what is known as a top pin structure in which thestorage layer 3 is formed on the underlying layer 5, and the fixed layer2 is formed on the nonmagnetic layer 4. The underlying layer 5 is usedto control crystallinity such as crystal orientation and crystal graindiameter of the layers higher than the storage layer 3. Detailedproperties of the underlying layer 5 will be described later. A caplayer 6 may be further formed on the fixed layer 2. The cap layer 6mainly function as a protective layer, for example, to prevent theoxidizing of the magnetic layers.

Second Embodiment

FIG. 2 is a sectional view of a magnetoresistive element according tothe second embodiment.

A magnetoresistive element 1A according to the second embodiment has theconfiguration of the magnetoresistive element 1 according to the firstembodiment shown in FIG. 1 wherein a storage layer 3 has a structure inwhich a magnetic film 3 a and a interface magnetic film 3 b thatcontacts a nonmagnetic layer 4 are stacked. The magnetic film 3 a andthe interface magnetic film 3 b are made of different materials.

The interface magnetic film 3 b is in contact with the nonmagnetic layer4, and therefore has the effect of lessening a lattice mismatch at theinterface. The use of a material having high spin polarization for theinterface magnetic film 3 b allows high tunneling magnetoresistanceratio (TMR ratio) and high spin transfer torque efficiency. Detailedproperties of the magnetic film 3 a and the interface magnetic film 3 bwill be described later.

Third Embodiment

FIG. 3 is a sectional view of a magnetoresistive element according tothe third embodiment.

A magnetoresistive element 1B according to the third embodiment has theconfiguration of the magnetoresistive element 1 according to the firstembodiment shown in FIG. 1 wherein a nonmagnetic layer 21 and a biaslayer (shift adjustment layer) 22 are inserted between a fixed layer 2and a cap layer 6.

The bias layer 22 is a perpendicular magnetization film made of aferromagnetic body and having a magnetization easy axis in the directionperpendicular to the film plane. The magnetization direction of the biaslayer 22 is fixed to a direction opposite (reverse or antiparallel) tothe magnetization direction of the fixed layer 2. The bias layer 22 hasthe effect of adjusting, to an opposite direction, an offset of storagelayer switching characteristics which results from a leakage magneticfield from the fixed layer 2 and which is a drawback when themagnetoresistive element is miniaturized. That is, the bias layer 22 hasthe effect of lessening and adjusting the shift of a switching currentof a storage layer 3 resulting from the leakage magnetic field from thefixed layer 2. Detailed properties of the nonmagnetic layer 21 and thebias layer 22 will be described later.

Fourth Embodiment

FIG. 4 is a sectional view of a magnetoresistive element according tothe fourth embodiment.

A magnetoresistive element 1C according to the fourth embodiment has theconfiguration of the magnetoresistive element 1A according to the secondembodiment shown in FIG. 2 wherein a nonmagnetic layer 21 and a biaslayer 22 are inserted between a fixed layer 2 and a cap layer 6.

In the magnetoresistive element 1C having such a configuration, aninterface magnetic film 3 b is in contact with a nonmagnetic layer 4,and therefore has the effect of lessening a lattice mismatch at theinterface, as in the second embodiment. Moreover, the use of a materialhaving high spin polarization for the interface magnetic film 3 b allowsa high TMR ratio and high spin transfer torque efficiency.

Furthermore, as in the third embodiment, the bias layer 22 is aperpendicular magnetization film made of a ferromagnetic body and havinga magnetization easy axis in the direction perpendicular to the filmplane. The magnetization direction of the bias layer 22 is fixed to adirection opposite to the magnetization direction of the fixed layer 2.The bias layer 22 has the effect of lessening and adjusting the shift ofa switching current of a storage layer 3 which results from the leakagemagnetic field from the fixed layer 2 and which is a drawback when theelement is fabricated.

Fifth Embodiment

FIG. 5 is a sectional view of a magnetoresistive element according tothe fifth embodiment.

A magnetoresistive element 1D according to the fifth embodiment has theconfiguration of the magnetoresistive element 1B according to the thirdembodiment shown in FIG. 3 wherein a third magnetic material film 2 dincluded in a fixed layer 2 is eliminated.

In the present embodiment, the magnetizations of the fixed layer 2 and abias layer 22 are magnetically coupled via a nonmagnetic layer 21 andare fixed to opposite directions. The bias layer 22 has the effect oflessening and adjusting the shift of a switching current of a storagelayer 3 which results from the leakage magnetic field from the fixedlayer 2 and which is a drawback when the element is fabricated.

Sixth Embodiment

FIG. 6 is a sectional view of a magnetoresistive element according tothe sixth embodiment.

A magnetoresistive element 1E according to the sixth embodiment has theconfiguration of the magnetoresistive element 1C according to the fourthembodiment shown in FIG. 4 wherein a third magnetic material film 2 dincluded in a fixed layer 2 is eliminated.

In the present embodiment, the magnetizations of the fixed layer 2 and abias layer 22 are magnetically coupled via a nonmagnetic layer 21 andare fixed to opposite directions. The configuration and advantageouseffects are similar in other respects to those according to the fourthembodiment.

In the first to sixth embodiments described above, what is known as atop pin structure has been shown in which the storage layer 3 is formedon the underlying layer 5 and the fixed layer 2 is formed on thenonmagnetic layer 4. Instead, what is known as a bottom pin structuremay be used in which the fixed layer 2 is formed on the underlying layer5 and the storage layer 3 is formed on the nonmagnetic layer 4.

Regarding Layers in the First to Sixth Embodiments

Now, the layers used in the first to sixth embodiments are describedbelow.

[1] Storage layer

First, the storage layer in the first to sixth embodiments is describedbelow. When a perpendicular magnetization film is used as the storagelayer 3, shape anisotropy is not used, as described above. Therefore,the element shape can be smaller than that of an in-plane magnetizationconfiguration. The use of a material having high perpendicular magneticanisotropy enables the maintenance of thermal disturbance resistance andalso enables both miniaturization and current reduction. The propertiesto be provided in the storage layer 3 and specific examples of materialsto be selected are described below in detail.

(1) Properties to be Provided in the Storage Layer

When a perpendicular magnetization material is used as the storage layer3, its thermal disturbance index A is represented as in Equation (1)below by taking the ratio between effective anisotropy energy (K_(u)^(eff)·V) and heat energy (k_(B)T).

Δ=K _(u) ^(eff) ·V/(k _(B) T)=(K _(u)−2πNM _(S) ²)·Va/(k _(B) T)  (1)

wherein

K_(u) ^(eff): effective perpendicular magnetic anisotropy

V: volume of perpendicular magnetization material

T: temperature of perpendicular magnetization material

k_(B): Boltzmann constant

K_(u): perpendicular magnetic anisotropy

M_(S): saturation magnetization

N: demagnetization factor

Va: magnetization reversal unit volume.

In order to avoid the problem of magnetization fluctuation caused byheat energy (thermal disturbance), the thermal disturbance index Apreferably shows a value higher than 60. However, if the element size orfilm thickness is reduced to allow for the increase of capacity, themagnetization reversal unit volume Va is reduced, and there is fear thatstorage cannot be maintained (=thermal disturbance) and becomesunstable. Therefore, it is preferable to select, for the storage layer3, a material high in perpendicular magnetic anisotropy K_(u) and/or lowin saturation magnetization M_(S).

In the meantime, a critical current I_(C) necessary for magnetizationreversal by the perpendicular magnetization type spin transfer torquewriting is generally proportional to α/(η·Δ), wherein

α: magnetic relaxation constant

η: spin transfer torque efficiency constant.

(2) Material of Storage Layer

As described above, in order for the storage layer 3 to be aperpendicular magnetization film and in order to enable both highthermal disturbance resistance and low-current magnetization reversal,it is preferable that the material of the storage layer has lowsaturation magnetization M_(S), has perpendicular magnetic anisotropyK_(u) high enough to maintain the thermal disturbance index Δ, and showshigh polarizability. A more detailed explanation is given below.

The storage layer 3 includes Co and Pd, an alloy containing Pt, or analloy in which 0 to 30 at % of boron (B) is added to one or more of Co,Fe, and Ni, or a stack structure of these materials. An underlying layerhaving an oriented close-packed face is properly selected as theunderlying layer 5 shown in FIG. 1 to FIG. 6 to control the crystalorientation of the storage layer 3 so that the storage layer 3 is aperpendicular magnetization film. Details of the underlying layer 5 andits specific manufacturing method will be described later.

FIG. 7 shows the Pd concentration dependence of the effectiveperpendicular magnetic anisotropy K_(u) ^(eff) of a CoPd film used asthe storage layer 3. The horizontal axis indicates the Pd concentration,and the vertical axis indicates the effective magnetic anisotropy K_(u)^(eff).

As apparent from FIG. 7, a Pd concentration of 30 at % or more permits ahigh perpendicular magnetic anisotropy of 1×10⁷ (erg/cm³) or more. Thishigh perpendicular magnetic anisotropy enables a magnetoresistiveelement showing high thermal stability to be provided despiteminiaturization. The storage layer 3 may contain additional elementssuch as Fe, Ni, B, and V.

[2] Fixed Layer

Now, the fixed layer 2 according to the first to sixth embodiments isdescribed. For the fixed layer 2, it is preferable to select a materialand a multilayer film structure which do not easily change themagnetization direction, in contrast to the storage layer 3. That is, itis preferable to select a material and a multilayer film structure whichare high in effective magnetic anisotropy K_(u)eff and saturationmagnetization M_(S) and which are high in magnetic relaxation constantα.

(1) Third Magnetic Material Film 2 d of Fixed Layer

The following materials are used for the third magnetic material film 2d that constitutes the fixed layer 2 in the first to fourth embodiments.

(a) Artificial Lattice

Artificial lattice includes a structure having alternately stackedlayers of an alloy (magnetic layer) which includes at least one of Fe,Co, and Ni and an alloy (nonmagnetic layer) which includes at least oneof Cr, Pt, Pd, Ag, Ir, Rh, Ru, Os, Re, Au, Cu, Gd, Tb, and Dy.

For example, such artificial lattice includes Co/Pt artificial lattice,Co/Pd artificial lattice, CoCr/Pt artificial lattice, Co/Ru artificiallattice, Co/Os artificial lattice, Co/Au artificial lattice, and Ni/Cuartificial lattice. Examples of an artificial lattice structure thatuses two magnetic layers include Co/Ni artificial lattice and Fe/Niartificial lattice. The effective magnetic anisotropy and the saturationmagnetization of such artificial lattice can be adjusted by adjustingthe addition of an element to the magnetic layer, the thickness ratiobetween the magnetic layer and the nonmagnetic layer, and the stackingperiod.

(b) Ordered Alloys

Ordered alloys include an alloy which includes one or more of Fe, Co,and Ni and which include one or more of Pt and Pd. The crystal structureof this alloy is an L1₀ ordered alloy. The L1₀ ordered alloy includes,for example, Fe₅₀Pt₅₀, Fe₅₀Pd₅₀, Co₅₀Pt₅₀, Fe₃₀Ni₂₀Pt₅₀, Co₃₀Fe₂₀Pt₅₀,and Co₃₀Ni₂₀Pt₅₀. The composition ratios in these ordered alloys areillustrative are not limited.

The effective magnetic anisotropy and the saturation magnetization canbe adjusted by adding, to these ordered alloys, an impurity element suchas Cu, Cr, Ag, or B, or an alloy of these elements, or an insulator.

(c) Disordered Alloys

Disordered alloys include a metal which includes cobalt (Co) as the maincomponent and which includes one or more of Cr, Ta, Nb, V, W, Hf, Ti,Zr, Pt, Pd, B, Fe, and Ni.

The disordered alloys include, for example, a CoCr alloy, a CoPt alloy,a CoCrPt alloy, a CoCrPtTa alloy, and a CoCrNb alloy. The effectivemagnetic anisotropy and the saturation magnetization of these alloys canbe adjusted by changing the ratio of a nonmagnetic element.

(d) Rare Earth Metal (RE)—Transition Metal (TM) Alloy

An alloy of a rare earth metal and a transition metal enables both aferrimagnetic material and a ferromagnetic material to be obtained bythe material of the rare earth metal.

Specific examples of the ferrimagnetic material include an alloy whichincludes Tb, Dy, or Gd, and an at least one of Fe, Co, and Ni. Suchferrimagnetic materials include, for example, TbFe, TbCo, TbFeCo,DyTbFeCo, and GdTbCo.

Specific examples of the ferromagnetic material include an alloy whichincludes Sm, Nd, Ho, and at least one of Fe, Co, and Ni. Suchferromagnetic materials include, for example, SmCo₅ and NdFeB. Themagnetic anisotropy and the saturation magnetization of these alloys canbe adjusted by adjusting the composition ratio.

(2) Stack Structure of Fixed Layer

The fixed layer 2 according to the first to fourth embodiments has astructure in which the first magnetic material film 2 a, the nonmagneticmaterial film 2 b, the second magnetic material film 2 c, and the thirdmagnetic material film 2 d are stacked in this order from the sidecontacting the nonmagnetic layer 4.

The first magnetic material film 2 a is made of a material including atleast one of Co, Fe, and Ni, or an alloy in which 0 to 30 at % of atleast one of B, Al, and Si is added to the above material, or amultilayer film structure that includes the above materials.

The nonmagnetic material film 2 b is made of a material comprising atleast one of Ta, Zr, Nb, Mo, Ru, Ti, V, Cr, W, Hf, Pt, Pd, Rh, and Ir.

The second magnetic material film 2 c is made of a material whichincludes Co as the main component and which may include, as anadditional element, at least one of Fe, Ni, B, Al, Si, Ta, Zr, Nb, Mo,Ru, Ti, V, Cr, W, and Hf.

In order to obtain a high TMR ratio and high heat treatment resistance,it is preferable that the Co concentration of the second magneticmaterial film 2 c is higher than the Co concentration of the firstmagnetic material film 2 a. For example, the surface of the secondmagnetic material film 2 c where the second magnetic material film 2 ccontacts the third magnetic material film 2 d is higher in Coconcentration than the surface of the first magnetic material film 2 awhere the nonmagnetic layer 4 contacts the first magnetic material film2 a.

FIG. 8A shows the dependence of the TMR ratio on the thickness of thesecond magnetic material film 2 c in the magnetoresistive element.Sample A is the magnetoresistive element in which the second magneticmaterial film 2 c is higher in Co concentration than the first magneticmaterial film 2 a. Sample B is the magnetoresistive element in which thesecond magnetic material film 2 c has the same Co concentration as thefirst magnetic material film 2 a.

It is apparent from FIG. 8A that Sample A shows higher TMR ratio thanSample B at all thickness. That is, Sample A shows a TMR ratio of 120%and satisfactory characteristics at a thickness of 5 Å to 30 Å. On theother hand, in Sample B, the magnetization easy axis of the fixed layer2 is in a in-plane direction when the thickness of the second magneticmaterial film 2 c is 13 Å. Therefore, the antiparallel magnetizationstate is not obtained, and no TMR ratio is obtained. It is found outfrom magnetization curves that, in the whole thickness region of SampleA, the fixed layer 2 is magnetized in the direction perpendicular to thefilm plane even if no external magnetic field is applied thereto.

FIG. 8B shows the change of the TMR ratio with the heat treatmenttemperature. The vertical axis indicates the TMR ratio after the heattreatment wherein the TMR ratio before the heat treatment is 1, and thehorizontal axis indicates the heat treatment temperature. Samples a, b,and c are produced from Sample A by setting the thickness of the secondmagnetic material film 2 c to 13 Å, 10 Å, and 4 Å, respectively. Sampled is produced from Sample B by setting the thickness of the secondmagnetic material film 2 c to 4 Å.

It is apparent from FIG. 8B that Samples a, b, and c is lower thanSample d in regard to the deterioration of the TMR ratio attributed tothe heat treatment. It is also apparent that in Samples a, b, and c, thedeterioration of the TMR ratio is reduced along with the increase ofthickness and the heat treatment resistance is improved.

However, it is found out that Sample c is greater than Samples a and bin the deterioration of the TMR ratio at 300° C. or more.

A magnetic field leaking to the storage layer increases if the thicknessof the second magnetic material film 2 c increases. Therefore, thethickness of the second magnetic material film 2 c cannot be more than20 Å. It is thus preferable that the thickness of the second magneticmaterial film 2 c is more than 4 Å and is 20 Å or less.

Here, a stack structure in which the first magnetic material film 2 a,the nonmagnetic material film 2 b, and the second magnetic material film2 c are stacked in this order from the side of the nonmagnetic layer 4is shown as an experimental example. However, similar advantageouseffects can also be expected by a stack structure having two or moremagnetic material films and two or more nonmagnetic material films, forexample, a stack structure comprising the first magnetic material film 2a, the nonmagnetic material film 2 b, the first magnetic material film 2a, the nonmagnetic material film 2 b, and the second magnetic materialfilm 2 c from the side of the nonmagnetic layer 4, or a stack structurecomprising the first magnetic material film 2 a, the nonmagneticmaterial film 2 b, the second magnetic material film 2 c, thenonmagnetic material film 2 b, and the second magnetic material film 2 cfrom the side of the nonmagnetic layer 4.

When a material higher in Co concentration than the first magneticmaterial film 2 a is used as the second magnetic material film 2 c andwhen the thickness of the second magnetic material film 2 c is 5 Å to 20Å, the concentration distributions and thickness of the first magneticmaterial film 2 a and the second magnetic material film 2 c that containC can be identified by an analysis that uses electron energy lossspectroscopy (TEM-EELS) for a transmission electron microscope orsecondary ion mass spectrometry (SIMS). Moreover, the concentrationdistributions and thickness can also be identified in themagnetoresistive element by using energy dispersive X-ray spectrometry(TEM-EDX).

In the fixed layer 2 according to fifth and sixth embodiments, theconstituent films other than a third magnetic material film 2 d have theabove-mentioned materials and characteristics, so that similaradvantageous effects can be expected.

(3) Interface Magnetic Films of Storage Layer and Fixed Layer

Here, the interface magnetic film is the first magnetic material film 2a that constitutes the fixed layer 2 in the first to sixth embodiments,and is the interface magnetic film 3 b that constitutes the storagelayer 3 in the second and fourth to sixth embodiments. These interfacemagnetic films have a configuration in which magnetic material layersand nonmagnetic material layers are repeatedly stacked for one or moreperiods. The interface magnetic film is an alloy which includes at leastone of Co, Fe, and Ni.

When oxides having an NaCl structure are used for the nonmagnetic layer4, the oxides having an NaCl structure allow a (100) face to be easilygrown as a preferential orientation face if crystals of these oxides aregrown

(i) on, for example, an amorphous CoFeNiB alloy which includes one ormore of Fe, Co, and Ni, or

(ii) on an alloy which has a body-centered cubic (BCC) structure andwhich has a (100) preferential orientation face and which includes oneor more of Fe, Co, and Ni. In particular, the (100) face can beextremely easily preferentially oriented on a CoFeX (X represents atleast one of the elements B, C, and N) amorphous alloy to which B, C, orN is added. It is therefore preferable that the magnetic material layercontacting the nonmagnetic layer 4 is an alloy(Co_(100-x)Fe_(x))_(100-y)B_(y)(0≦y≦30 at %) which contains Co, Fe, andNi.

An element having a high melting point which includes at least one ofTa, W, Hf, Zr, Nb, Mo, Ti, V, and Cr, or an alloy of these elements ispreferably used for the nonmagnetic material layer included in theinterface magnetic film. When Ta is used for the nonmagnetic materiallayer and CoFeB is used for the magnetic material layer, thedistribution shows that the concentration of B is higher at pointscloser to the Ta layer because B in CoFeB of the magnetic material layeris drawn to Ta after the heat treatment.

The interface magnetic film has a configuration in which magneticmaterial layers and nonmagnetic material layers are repeatedly stackedfor one or more periods. The magnetic material layer preferably hasmagnetic exchange coupling via the nonmagnetic material layer, that thenonmagnetic material layer is preferably 10 Å or less and particularlypreferably 5 Å or less. This permits the magnetization direction of theinterface magnetic film to be aligned with the magnetization directionsof the magnetic film 3 a and the magnetic film 2 a.

[3] Underlying Layer

As in the above description of the storage layer, it is necessary tohave a structure that allows an atom dense face to be easily oriented,in order to form a perpendicular magnetization film having amagnetization easy axis in the direction perpendicular to the filmplane. That is, the crystal orientation needs to be controlled so thatthe (111) face of the face-centered cubic (FCC) structure and the (001)face of a hexagonal close-packed (HCP) structure are oriented.Therefore, the selection of an underlying layer material and a stackconfiguration is important.

(1) Stack Configuration of Underlying Layer

FIG. 9 is a sectional view of a stack structure comprising theunderlying layer 5 and the storage layer 3 in the magnetoresistiveelement according to the embodiment.

In this stack structure, for example, Ta having a thickness of about 5nm is provided as a contact layer 8 between a lower electrode 7 and theunderlying layer 5. The underlying layer 5 has a stack structure inwhich underlying films 5 a, 5 b, and 5 c are stacked in this order. Forexample, a CoPd layer having a thickness of about 2 nm is provided asthe storage layer 3 on the underlying layer 5. The configuration abovethe storage layer 3 is as shown in FIG. 1 to FIG. 6.

In the magnetoresistive element according to the first to sixthembodiments, the underlying film 5 c included in the underlying layer 5is preferably made of a metal material that lattice-matches the storagelayer 3. The underlying film 5 a preferably include a material and aconfiguration that allow the underlying films 5 b and 5 c to be smoothand to be improved in crystal orientation. The underlying films 5 b and5 c are preferably made of a Ru layer having a thickness of about 3 nmand a Pt layer having a thickness of about 3 nm, respectively.

(2) Material of Underlying Layer

Now, specific materials of the underlying films 5 a, 5 b, and 5 c thatconstitute the underlying layer 5 are described.

A metal having a dense structure is used as the underlying film 5 c.Metals which lattice-match the storage layer 3, for example, a CoPdalloy or a CoPt alloy and which have a close-packed structure include,for example, Pt, Pd, Ir, and Ru. For example, instead of one metalelement, an alloy comprising two metal elements such as Pt—Pd or Pt—Iror three or more metal elements may be used. It is also possible to usealloys of the above-mentioned metals and fcc metals such as Cu, Au, andAl: Pt—Cu, Pd—Cu, Ir—Cu, Pt—Au, Ru—Au, Pt—Al, and Ir—Al, or to usealloys of Re, Ti, Zr, and Hf and hcp metals: Pt—Re, Pt—Ti, Ru—Re, Ru—Ti,Ru—Zr, and Ru—Hf.

As an extremely large thickness of the underlying layer 5 leads to lowersmoothness, the thickness range of the underlying layer 5 is preferably30 nm or less. The underlying films 5 b and 5 c are stacked in order tostack materials having different lattice constants so that the latticeconstant is adjusted before the formation of a CoPd alloy or a CoPtalloy. For example, if Ru is formed for the underlying film 5 b and Ptis formed for the underlying film 5 c, Pt of the underlying film 5 cwill have a lattice constant different from a bulk lattice constant dueto Ru of the underlying film 5 b. However, as described above, thelattice constant can be adjusted even when an alloy is used. Therefore,one of the underlying films 5 b and 5 c can be omitted.

In the underlying layer 5, the underlying film 5 a is used to improvesmoothness and to improve the crystal orientation of the metals of theunderlying films 5 b and 5 c having close-packed structures. Morespecifically, Ta, for example, is used for the underlying film 5 a. Ifthe thickness of the underlying film 5 a is too large, it takes a longtime to form the underlying film 5 a, leading to lower productivity. Ifthe thickness of the underlying film 5 a is too small, theabove-mentioned effect of controlling orientation is lost. It istherefore preferable that the thickness of the underlying film 5 aranges from 1 nm to 10 nm.

[4] Nonmagnetic Layer

The material of the nonmagnetic layer 4 in the first to sixthembodiments is preferably an oxide having an NaCl structure. Such anoxide includes, for example, MgO, CaO, SrO, TiO, VO, and NbO. Theseoxides having an NaCl structure allow a (100) face to be easily grown asa preferential orientation face if crystals of these oxides are grown

(i) on, for example, an amorphous CoFeNiB alloy which includes, as themain component, one or two or more of Fe, Co, and Ni, or

(ii) on an alloy which has a body-centered cubic (BCC) structure andwhich has a (100) preferential orientation face and which includes, asthe main component, one or two or more of Fe, Co, and Ni.

In particular, the (100) face can be extremely easily preferentiallyoriented on a CoFeX (X represents at least one of the elements B, C, andN) amorphous alloy to which B, C, or N is added.

When the magnetization direction of the storage layer 3 is antiparallelto the magnetization direction of the fixed layer 2, a spin-polarized Δ₁band takes charge of tunneling conduction. Therefore, majority spinelectrons alone contribute to conduction. As a result, themagnetoresistive element decreases in conductivity and increases inresistance value.

On the contrary, when the magnetization direction of the storage layer 3is parallel to the magnetization direction of the fixed layer 2, a Δ₅band that is not spin-polarized dominates conduction. Therefore, themagnetoresistive element increases in conductivity and decreases inresistance value. Thus, the formation of the Δ₁ band is the point indeveloping a high TMR ratio. In order to form the Δ₁ band, theinterfaces between the (100) face of the nonmagnetic layer 4 made of anoxide having an NaCl structure and the storage layer 3 as well as thefixed layer 2 have to be well consistent.

It is preferable that the storage layer and the fixed layer have stackstructures as described above to further improve the lattice match inthe (100) face of the nonmagnetic layer 4 made of an oxide layer havingan NaCl structure. From the viewpoint of forming the Δ₁ band, it ispreferable that such materials that the lattice mismatch in the (100)face of the nonmagnetic layer 4 is 5% or less are selected as theinterface magnetic film 3 b that constitutes the storage layer 3 and theinterface magnetic film 2 a that constitutes the fixed layer 2.

[5] Bias layer

As shown in FIG. 3 to FIG. 6, the nonmagnetic layer 21 and the biaslayer (shift adjustment layer) 22 may be disposed between the fixedlayer 2 and the cap layer 6. This makes it possible to lessen and adjustof the shift of a switching current of the storage layer 3 resultingfrom the leakage magnetic field from the fixed layer 2.

It is preferable that the nonmagnetic layer 21 has thermal resistancethat prevents the fixed layer 2 and the bias layer 22 from being mixedby a thermal process and also has a function to control crystalorientation during the formation of the bias layer 22. As the increaseof the thickness of the nonmagnetic layer 21 increases the distancebetween the bias layer 22 and the storage layer 3, a shift adjustmentmagnetic field applied to the storage layer 3 from the bias layer 22 isreduced. It is therefore preferable that the thickness of thenonmagnetic layer 21 is 5 nm or less.

The bias layer 22 is made of a ferromagnetic body having a magnetizationeasy axis in the direction perpendicular to the film plane. Morespecifically, the materials listed for the fixed layer 2 can be used.However, as the bias layer 22 is farther from the storage layer 3 thanthe fixed layer 2, the thickness or the saturation magnetization M_(S)of the bias layer 22 needs to be set to be more than that of the fixedlayer 2 so that the leakage magnetic field applied to the storage layer3 is adjusted by the bias layer 22.

That is, Equation (2) below needs to be satisfied

M_(S2)×t₂<M_(S22)×t₂₂  (2)

wherein t₂ and M_(S2) are the thickness or the saturation magnetizationof the fixed layer 2, and t₂₂ and M_(S22) are the thickness or thesaturation magnetization of the bias layer 22.

For example, suppose that the element is fabricated into a size of 50nm. In this case, a magnetic material having a saturation magnetizationM_(S) of 1000 emu/cm³ and a thickness of 5 nm is used for the fixedlayer 2 to offset the shift of the switching current. Accordingly, therequired characteristics are as follows: The thickness of thenonmagnetic layer 21 is 3 nm. The saturation magnetization M_(S) of thebias layer 22 is 1000 emu/cm³. The thickness of the bias layer 22 isabout 15 nm.

In order to obtain the effect of canceling the above-mentioned shift ofthe switching current, the magnetization directions of the fixed layer 2and the bias layer 22 need to be set to be antiparallel to each other.To satisfy this relation, it is possible to select such materials thatthe coercive force H_(c2) of the fixed layer 2 and the coercive forceH_(c22) of the bias layer 22 satisfy the relation H_(c2)>H_(c22) orH_(c2)<H_(c22). In this case, the magnetization directions of the fixedlayer 2 and the bias layer 22 can be set to be antiparallel to eachother by switching the magnetization direction of the layer lower incoercive force by minor loop magnetization in advance.

The magnetization directions of the fixed layer 2 and the bias layer 22can also be set to be antiparallel to each other by the syntheticanti-ferromagnetic (SAF) coupling of the fixed layer 2 and the biaslayer 22 via the nonmagnetic layer 21.

More specifically, Ru, for example, is used as the material of thenonmagnetic layer 21 so that the magnetization directions of the fixedlayer 2 and the bias layer 22 can also be coupled to be antiparallel toeach other. Thus, the magnetic field leaking from the fixed layer 2 canbe reduced by the bias layer 22, so that the shift of the switchingcurrent of the storage layer 3 can be reduced. As a result,element-to-element variation of the switching current of the storagelayer 3 can also be reduced.

Although the nonmagnetic layer 21 and the bias layer 22 are disposedbetween the fixed layer 2 and the cap layer 6 in the example describedabove, the nonmagnetic layer and the bias layer (shift adjustment layer)may be disposed between the storage layer 3 and the underlying layer 5.In this case, the shift of the switching current of the storage layer 3resulting from the leakage magnetic field from the fixed layer 2 can belessened and adjusted. The nonmagnetic layers and the bias layers (shiftadjustment layers) may be disposed between the fixed layer 2 and the caplayer 6 and between the storage layer 3 and the underlying layer 5.

As described above, according to the first to sixth embodiments, the Coconcentration of the second magnetic material film 2 c included in thefixed layer 2 is higher than the Co concentration of the first magneticmaterial film 2 a, and the thickness of the second magnetic materialfilm 2 c is larger, so that it is possible to provide a magnetoresistiveelement which shows only a slight change in electric characteristics inresponse to a heat treatment after film formation and which has highthermal resistance. That is, it is possible to provide amagnetoresistive element for the spin transfer torque writing methodwhich is thermally stable and which can inhibit the decrease of themagnetoresistance ratio.

Seventh Embodiment

A magnetic random access memory (MRAM) according to the seventhembodiment is described with reference to FIG. 10 and FIG. 11. The MRAMaccording to the seventh embodiment is configured to use themagnetoresistive element according to one of the first to sixthembodiments as a storage element. In the embodiment described below, themagnetoresistive element 1 according to the first embodiment is used asa magnetoresistive element.

FIG. 10 is a circuit diagram showing the configuration of the MRAMaccording to the seventh embodiment.

The MRAM according to the seventh embodiment includes a memory cellarray 40 having memory cells MC arranged in matrix form. Pairs of bitlines BL, /BL are provided in the memory cell array 40 to extend in acolumn direction. Word lines WL are also provided in the memory cellarray 40 to extend in a row direction.

A memory cell MC is located at the intersection of the bit line BL andthe word line WL. Each memory cell MC includes the magnetoresistiveelement 1 and a select transistor (e.g. n-channel MOS transistor) 41.One end of the magnetoresistive element 1 is connected to the bit lineBL. The other end of the magnetoresistive element 1 is connected to thedrain terminal of the select transistor 41. The source terminal of theselect transistor 41 is connected to the bit line /BL. The gate terminalof the select transistor 41 is connected to the word line WL.

A row decoder 42 is connected to the word line WL. A write circuit 44and a read circuit 45 are connected to the pairs of bit lines BL, /BL. Acolumn decoder 43 is connected to the write circuit 44 and the readcircuit 45. Each memory cell MC is selected by the row decoder 42 andthe column decoder 43.

Data is written into the memory cell MC as follows. First, in order toselect a memory cell MC to write data into, the word line WL connectedto this memory cell MC is activated. As a result, the select transistor41 is turned on.

Here, a bi-directional write current Iw is supplied to themagnetoresistive element 1 in accordance with the data to be written.More specifically, when the write current Iw is supplied to themagnetoresistive element 1 from left to right, the write circuit 44applies a positive voltage to the bit line BL, and applies a groundvoltage to the bit line /BL. When the write current Iw is supplied tothe magnetoresistive element 1 from right to left, the write circuit 44applies a positive voltage to the bit line /BL, and applies a groundvoltage to the bit line BL. In this way, data “0” or data “1” can bewritten into the memory cell MC.

Data is read from the memory cell MC as follows. First, the selecttransistor 41 of a memory cell MC to be selected is turned on. The readcircuit 45 supplies the magnetoresistive element 1 with, for example, aread current Ir running from right to left, that is, supplies the readcurrent Ir from the bit line /BL to the bit line BL. The read circuit 45detects the resistance value of the magnetoresistive element 1 inaccordance with the read current Ir. Further, the read circuit 45 readsdata stored in the magnetoresistive element 1 from the detectedresistance value.

Now, the structure of the MRAM according to the embodiment is describedwith reference to FIG. 11. FIG. 11 is a sectional view showing thestructure of one memory cell MC.

As shown, the memory cell MC has the magnetoresistive element (MTJ) 1and the select transistor 41. An element isolation insulating layer 46is provided in the surface area of a p-type semiconductor substrate 51.The surface area of the semiconductor substrate 51 in which the elementisolation insulating layer 46 is not provided is an element area (activearea) in which elements are formed. The element isolation insulatinglayer 46 includes, for example, shallow trench isolation (STI). Forexample, silicon oxide is used for the STI.

A source area S and a drain area D that are separated from each otherare formed in the element area of the semiconductor substrate 51. Thesource area S and the drain area D include n+ type diffusion areasformed by introducing a high-concentration impurity, for example, an n+type impurity into the semiconductor substrate 51.

A gate insulating film 41A is formed on the semiconductor substrate 51between the source area S and the drain area D. A gate electrode 41B isformed on the gate insulating film 41A. This gate electrode 41Bfunctions as the word line WL. Thus, the select transistor 41 isprovided on the semiconductor substrate 51.

A interconnect layer 53 is formed on the source area S via a contact 52.The interconnect layer 53 functions as the bit line /BL. A leader line55 is formed above the drain area D via a contact 54. Themagnetoresistive element 1 intervening between a lower electrode 7 andan upper electrode 9 is provided above the leader line 55. Ainterconnect layer 56 is formed on the upper electrode 9. Theinterconnect layer 56 functions as the bit line BL. The space betweenthe semiconductor substrate 51 and the interconnect layer 56 is filledwith an interlayer insulating film 57 made of, for example, siliconoxide.

As described above in detail, according to the seventh embodiment, anMRAM can be configured by using the magnetoresistive element 1. Themagnetoresistive element 1 can be used not only as a magnetic memory ofa spin transfer torque writing type but also as a magnetic domain wallmotion magnetic memory.

The MRAM shown in the seventh embodiment is applicable to variousdevices. Several applications of the MRAM are described below.

[1] Application 1

FIG. 12 shows an extracted DSL data path unit of a digital subscriberline (DSL) modem.

This modem includes, for example, a programmable digital signalprocessor (DSP) 100, an analog-digital (A/D) converter 110, adigital-analog (D/A) converter 120, a transmission driver 130, and areceiver amplifier 140.

A band pass filter is not shown in FIG. 12. Instead, an MRAM 170according to the seventh embodiment and an electrically erasable andprogrammable ROM (EEPROM) 180 are shown as various types of optionalmemories for holding a line code program (program which is executed bythe DSP and which selects and operates the modem in accordance with, forexample, coded subscriber's line information and transmission conditions(line code: QAM, CAP, RSK, FM, AM, PAM, or DWMT)).

Although two kinds of memories: the MRAM 170 and the EEPROM 180 are usedas the memories for holding the line code program in this application,the EEPROM 180 may be replaced by an MRAM. That is, the MRAM alone maybe used instead of using two kinds of memories.

[2] Application 2

FIG. 13 shows a mobile telephone terminal 300 as another application.

A communication section 200 that enables a communication functionincludes, for example, a sending/receiving antenna 201, an antennaduplexer 202, a receiver 203, a baseband processor 204, a digital signalprocessor (DSP)205 used as an audio codec, a speaker (receiver) 206, amicrophone (transmitter) 207, a transmitter 208, and a frequencysynthesizer 209.

The mobile telephone terminal 300 is also provided with a controlsection 220 for controlling the components of the mobile telephoneterminal 300. The control section 220 is a microcomputer which is formedby connecting a CPU 221, a ROM 222, an MRAM 223 according to the seventhembodiment, and a flash memory 224 via a bus 225.

Programs to be executed by the CPU 221 and necessary display data suchas fonts are stored in the ROM 222 in advance.

The MRAM 223 is mainly used as a work area, and is used by the CPU 221to store, as needed, data being calculated during the execution of theprogram, or used to temporarily store data exchanged between the controlsection 220 and each component.

The flash memory 224 is used to store setting parameters so that even ifthe mobile telephone terminal 300 is powered off, conditions setimmediately before the power-off are stored to enable the same settingwhen the mobile telephone terminal 300 is powered on next. This preventsthe disappearance of the stored setting parameters even if the mobiletelephone terminal 300 is powered off.

The mobile telephone terminal 300 is also provided with an audio datareproduction processor 211, an external output terminal 212, an LCDcontroller 213, a liquid crystal display (LCD) 214 for display, and aringer 215 which generates a ringing tone.

The audio data reproduction processor 211 reproduces audio data input tothe mobile telephone terminal 300 (or audio information (audio data)stored in a later-described external memory 240). The reproduced audiodata (audio information) can be transmitted to a headphone or a mobilespeaker via the external output terminal 212 and thereby taken out.

Thus, the audio information can be reproduced by providing the audiodata reproduction processor 211. The LCD controller 213 receives, forexample, display information from the CPU 221 via the bus 225, convertsthe display information to LCD control information for controlling theLCD 214, and drives the LCD 214 to display the information.

Furthermore, the mobile telephone terminal 300 is provided withinterface circuits (I/F) 231, 233, and 235, the external memory 240, anexternal memory slot 232, a key operation unit 234, and an externalinput/output terminal 236. The external memory 240, for example, amemory card is inserted into the external memory slot 232. The externalmemory slot 232 is connected to the bus 225 via the interface circuit(I/F) 231.

The slot 232 is thus provided in the mobile telephone terminal 300 suchthat information in the mobile telephone terminal 300 can be writteninto the external memory 240 or information (e.g. audio information)stored in the external memory 240 can be input to the mobile telephoneterminal 300.

The key operation unit 234 is connected to the bus 225 via the interfacecircuit (I/F) 233. Key input information input from the key operationunit 234 is transmitted to, for example, the CPU 221. The externalinput/output terminal 236 is connected to the bus 225 via the interfacecircuit (I/F) 235. The external input/output terminal 236 functions as aterminal for inputting various kinds of information to the mobiletelephone terminal 300 from the outside or outputting information fromthe mobile telephone terminal 300 to the outside.

Although the ROM 222, the MRAM 223, and the flash memory 224 are used inthis application, the flash memory 224 may be replaced by an MRAM, andthe ROM 222 can also be replaced by an MRAM.

[3] Application 3

FIG. 14 to FIG. 18 respectively show examples of how the MRAM is appliedto cards (MRAM cards) such as smart media for storing media content.

As shown in FIG. 14, an MRAM card body 400 has an MRAM chip 401 therein.The card body 400 has an opening 402 formed in a position correspondingto the MRAM chip 401 so that the MRAM chip 401 is exposed. This opening402 is provided with a shutter 403 so that the MRAM chip 401 isprotected by the shutter 403 when the MRAM card is carried. The shutter403 is made of a material such as ceramics having the effect of blockingan external magnetic field.

In order to transfer data, the shutter 403 is opened to expose the MRAMchip 401. An external terminal 404 takes out content data stored in theMRAM card.

FIG. 15 and FIG. 16 show a card insertion type transfer device fortransferring data to the MRAM card.

A data transfer device 500 has a storage portion 500 a. A first MRAMcard 550 is stored in the storage portion 500 a. The storage portion 500a is provided with an external terminal 530 which is electricallyconnected to the first MRAM card 550. This external terminal 530 is usedto rewrite data in the first MRAM card 550.

A second MRAM card 450 used by an end user is inserted from an insertionportion 510 of the data transfer device 500 as indicated by an arrow,and pushed in until stopped by a stopper 520. This stopper 520 alsoserves as a member to align the first MRAM card 550 with the second MRAMcard 450. When the second MRAM card 450 is located in a predeterminedposition, a control signal is supplied to the external terminal 530 froma first MRAM data rewrite controller, and data stored in the first MRAMcard 550 is transferred to the second MRAM card 450.

FIG. 17 is a sectional view showing a fit type transfer device fortransferring data to the MRAM card.

A transfer device 600 is a type that mounts the second MRAM card 450 onthe first MRAM card 550 in a fitting manner using the stopper 520 as amark, as indicated by an arrow. The transfer method is the same as thatof the card insertion type and is therefore not described.

FIG. 18 is a sectional view showing a slide type transfer device fortransferring data to the MRAM card.

A transfer device 700 is provided with a tray slide 560 as in a CD-ROMdrive or a DVD drive. This tray slide 560 moves as indicated by anarrow. When the tray slide 560 has moved to the position indicated by abroken line, the second MRAM card 450 is mounted on the tray slide 560,and the tray slide 560 then moves to convey the second MRAM card 450into the transfer device 700.

The slide type transfer device is the same as the card insertion typetransfer device in that the second MRAM card 450 is conveyed so that thetip of the second MRAM card 450 comes into contact with the stopper 520,and in the transfer method. Therefore, no explanations are given inthese respects.

The MRAM described in the seventh embodiment can be used in a filememory capable of high-speed random writing, a mobile terminal capableof high-speed downloading, a mobile player capable of high-speeddownloading, a semiconductor memory for broadcasting devices, a driverecorder, a home video, a high-capacity buffer memory for communication,and a semiconductor memory for a security camera, thus providing manyindustrial advantages.

As described above, according to the embodiments, it is possible toprovide a magnetoresistive element for the spin transfer torque writingmethod which is thermally stable and which can inhibit the decrease ofthe magnetoresistance ratio, and also provide a magnetic memory thatuses such a magnetoresistive element.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

1. A magnetoresistive element comprising: a first magnetic layer havingan axis of easy magnetization perpendicular to a film plane, and aninvariable magnetization direction; a second magnetic layer having anaxis of easy magnetization perpendicular to a film plane, and a variablemagnetization direction; and a nonmagnetic layer provided between thefirst magnetic layer and the second magnetic layer, wherein the firstmagnetic layer has a structure in which a first magnetic material film,a nonmagnetic material film, a second magnetic material film, and athird magnetic material film are stacked, the first magnetic materialfilm is provided in contact with the nonmagnetic layer, the nonmagneticmaterial film is provided in contact with the first magnetic materialfilm, the second magnetic material film is provided in contact with thenonmagnetic material film, and the third magnetic material film isprovided in contact with the second magnetic material film, the secondmagnetic material film has a Co concentration higher than that of thefirst magnetic material film, and a current is passed across the firstmagnetic layer and the second magnetic layer via the nonmagnetic layerso that the magnetization direction of the second magnetic layer varies.2. The magnetoresistive element according to claim 1, wherein thesurface of the second magnetic material film where the second magneticmaterial film contacts the third magnetic material film is higher in Coconcentration than the surface of the first magnetic material film wherethe nonmagnetic layer contacts the first magnetic material film.
 3. Themagnetoresistive element according to claim 1, wherein the thickness ofthe second magnetic material film is more than 4 Å and is 20 Å or less.4. The magnetoresistive element according to claim 1, wherein the secondmagnetic layer comprises two films different in material.
 5. Themagnetoresistive element according to claim 4, wherein the two filmsinclude a magnetic film and an interface magnetic film, and theinterface magnetic film is located between the nonmagnetic layer and themagnetic film.
 6. The magnetoresistive element according to claim 5,wherein the interface magnetic film includes a structure in which amagnetic material layer and a nonmagnetic material layer are stacked forat least one period.
 7. The magnetoresistive element according to claim1, further comprising: a third magnetic layer located on a surface ofthe first magnetic layer, which is opposite to a surface where thenonmagnetic material layer is located, wherein the third magnetic layerhas a magnetization direction antiparallel to the magnetizationdirection of the first magnetic layer.
 8. The magnetoresistive elementaccording to claim 1, further comprising: a fourth magnetic layerlocated on a surface of the second magnetic layer, which is opposite toa surface where the nonmagnetic material layer is located, wherein thefourth magnetic layer has a magnetization direction antiparallel to themagnetization direction of the first magnetic layer.
 9. Themagnetoresistive element according to claim 1, wherein the thirdmagnetic material film comprises an artificial lattice structure or analloy which includes at least one of Fe, Co, and Ni and at least one ofCr, Pt, Pd, Ag, Ir, Rh, Ru, Os, Re, Au, Cu, Gd, Tb, and Dy.
 10. Themagnetoresistive element according to claim 1, wherein the thirdmagnetic material film comprises an alloy which includes at least one ofFe, Co, and Ni and at least one of Pt and Pd.
 11. The magnetoresistiveelement according to claim 1, wherein the first magnetic material filmincludes a structure in which a magnetic material layer and anonmagnetic material layer are stacked for at least one period.
 12. Themagnetoresistive element according to claim 1, wherein the firstmagnetic material film comprises a material including at least one ofCo, Fe, and Ni, or an alloy in which at least one of B, Al, and Si isadded to the material.
 13. The magnetoresistive element according toclaim 1, wherein the second magnetic material film comprises a materialwhich includes Co as the main component and comprises at least one ofFe, Ni, B, Al, Si, Ta, Zr, Nb, Mo, Ru, Ti, V, Cr, W, and Hf.
 14. Themagnetoresistive element according to claim 1, wherein the nonmagneticmaterial film comprises at least one of Ta, Zr, Nb, Mo, Ru, Ti, V, Cr,W, and Hf.
 15. A magnetoresistive element comprising: a first magneticlayer having an axis of easy magnetization perpendicular to a filmplane, and an invariable magnetization direction; a second magneticlayer having an axis of easy magnetization perpendicular to a filmplane, and a variable magnetization direction; and a nonmagnetic layerprovided between the first magnetic layer and the second magnetic layer,wherein the first magnetic layer includes a structure in which a firstmagnetic material film, a nonmagnetic material film, and a secondmagnetic material film are stacked, the first magnetic material film isprovided in contact with the nonmagnetic layer, the nonmagnetic materialfilm is provided in contact with the first magnetic material film, andthe second magnetic material film is provided in contact with thenonmagnetic material film, the second magnetic material film has a Coconcentration higher than that of the first magnetic material film, anda current is passed across the first magnetic layer and the secondmagnetic layer via the nonmagnetic layer so that the magnetizationdirection of the second magnetic layer varies.
 16. The magnetoresistiveelement according to claim 15, wherein the surface of the secondmagnetic material film is higher in Co concentration than the surface ofthe first magnetic material film where the nonmagnetic layer contactsthe first magnetic material film.
 17. The magnetoresistive elementaccording to claim 15, wherein the thickness of the second magneticmaterial film is more than 4 Å and is 20 Å or less.
 18. A magneticmemory comprising: a memory cell including the magnetoresistive elementaccording to claim 1; a first interconnect to which one end of themagnetoresistive element is electrically connected; and a secondinterconnect to which the other end of the magnetoresistive element iselectrically connected.
 19. The magnetoresistive element according toclaim 18, further comprising a select transistor provided between oneend of the magnetoresistive element and the first interconnect.